KR20240009876A - Lithium secondary battery - Google Patents

Abstract

The present invention provides a non-aqueous electrolyte solution containing a lithium salt, an organic solvent, a first additive represented by Formula 1, and a second additive represented by Formula 2; A positive electrode containing a positive electrode active material; A negative electrode containing a negative electrode active material made of silicon; and a lithium secondary battery comprising a separator interposed between the positive electrode and the negative electrode.

Description

Lithium secondary battery {LITHIUM SECONDARY BATTERY}

The present invention relates to a lithium secondary battery comprising an electrolyte solution containing a specific additive combination and a pure silicon (Pure Si) anode material.

Lithium secondary batteries generally form an electrode assembly by interposing a separator between a positive electrode containing a positive electrode active material made of a transition metal oxide containing lithium and a negative electrode containing a negative electrode active material capable of storing lithium ions, and the electrode It is manufactured by inserting the assembly into a battery case, injecting an electrolyte that serves as a medium for transferring lithium ions, and then sealing it.

Lithium secondary batteries can be miniaturized and have high energy density and operating voltage, so they are applied to various fields such as mobile devices, electronic products, and electric vehicles. As the application fields of lithium secondary batteries become more diverse, the required physical properties are gradually increasing, and in particular, the development of lithium secondary batteries that can be operated stably even under high temperature conditions is required.

Meanwhile, when a lithium secondary battery is operated under high temperature conditions, PF ₆ ^- anions may be thermally decomposed from lithium salts such as LiPF ₆ contained in the electrolyte to generate Lewis acids such as PF ₅ , which may react with moisture to form HF. Create it. Decomposition products such as PF ₅ and HF can not only destroy the film formed on the electrode surface, but also cause a decomposition reaction of the organic solvent and react with the decomposition products of the positive electrode active material to elute transition metal ions. The eluted transition metal ions may be electrodeposited on the cathode and destroy the film formed on the cathode surface.

If the electrolyte decomposition reaction continues on the destroyed film, the performance of the battery further deteriorates. Therefore, there is a demand for the development of a secondary battery that can maintain excellent performance even under high temperature conditions.

KR 10-2022-0033455 A

The present invention is intended to solve the above problems, and seeks to improve the high-temperature performance of a lithium secondary battery containing pure silicon anode active material by introducing a non-aqueous electrolyte containing a combination of two specific additives.

According to one embodiment, the present invention,

A non-aqueous electrolyte solution containing a lithium salt, an organic solvent, a first additive represented by the following Chemical Formula 1, and a second additive represented by the following Chemical Formula 2;

A positive electrode containing a positive electrode active material;

A negative electrode containing a negative electrode active material made of silicon; and

A lithium secondary battery including a separator interposed between the positive electrode and the negative electrode is provided.

[Formula 1]

In Formula 1,

A is a heterocyclic group having 3 to 5 carbon atoms or a heteroaryl group having 3 to 5 carbon atoms,

R1 is an alkylene group having 1 to 3 carbon atoms,

[Formula 2]

In Formula 2,

R2 is an alkyl group having 1 to 10 carbon atoms substituted with one or more fluorines.

The lithium secondary battery according to the present invention can improve the high-temperature lifespan and gas generation amount of a lithium secondary battery containing a silicon negative electrode active material by including a non-aqueous electrolyte solution containing a specific additive combination.

Hereinafter, the present invention will be described in more detail.

In general, anions contained in lithium salts such as LiPF ₆ , which are widely used in electrolytes for lithium secondary batteries, form decomposition products such as hydrogen fluoride (HF) and PF ₅ due to thermal decomposition or moisture, and this phenomenon occurs when operating under high temperature conditions. It gets worse. Since the decomposition product has acid properties, it deteriorates the electrode surface properties within the battery.

Due to electrolyte decomposition products and changes in the structure of the anode due to repeated charging and discharging, the transition metals in the anode are easily eluted into the electrolyte, and the eluted transition metals are re-deposited on the anode, increasing the resistance of the anode. .

In addition, when the eluted transition metal moves to the cathode through the electrolyte, it is electrodeposited on the cathode, causing destruction of the SEI (solid electrolyte interphase) film and additional electrolyte decomposition reaction, which causes problems such as consumption of lithium ions and increased resistance. .

In particular, when silicon (Si) is used as a negative electrode active material, the SEI film is easily damaged and regenerated continuously due to large volume changes during the charging and discharging process, which causes problems such as deterioration of battery durability and intensification of gas generation. there is.

In order to solve this problem, the present inventors included a first additive represented by Formula 1 below and a second additive represented by Formula 2 below into a non-aqueous electrolyte solution, thereby forming a strong SEI film on the cathode, thereby improving the battery. It was found that performance, especially the amount of high-temperature gas generation, could be improved.

Hereinafter, each component of the present invention will be described in more detail.

non-aqueous electrolyte

The lithium secondary battery according to the present invention includes a non-aqueous electrolyte solution containing a lithium salt, an organic solvent, a first additive represented by the following Chemical Formula 1, and a second additive represented by the following Chemical Formula 2.

Below, each component of the non-aqueous electrolyte solution is explained in detail.

(1) First additive and second additive

The non-aqueous electrolyte solution of the present invention includes a first additive represented by the following formula (1).

[Formula 1]

In Formula 1,

A is a heterocyclic group having 3 to 5 carbon atoms or a heteroaryl group having 3 to 5 carbon atoms,

R1 is an alkylene group having 1 to 3 carbon atoms.

The first additive represented by Formula 1 contains a Propargyl functional group, so when it is included in the electrolyte, it is reduced and decomposed through a radical reaction, forming an SEI film of PEO (poly(ethylene oxide))-based polymer on the cathode surface. can be formed. This not only improves the high-temperature durability of the cathode itself, but also prevents electrodeposition of transition metals on the cathode surface. In addition, since the propargyl group has the property of adsorbing to metal ions, it is adsorbed on the surface of metallic impurities contained in the anode to prevent elution of the impurities, and prevents the eluted metal ions from precipitating on the cathode, thereby preventing internal short-circuiting. It can have a suppressing function. In addition, the first additive binds to PF ₅ , a decomposition product of the electrolyte, to suppress the production of HF, thereby preventing destruction of the cathode electrolyte interphase (CEI) film formed on the anode surface and suppressing further decomposition of the electrolyte.

In one embodiment of the present invention, A of Formula 2 may be a nitrogen-containing heteroaryl group having 3 to 5 carbon atoms, and preferably an imidazole group.

As a preferred example, the first additive may be represented by the following formula 1-1.

[Formula 1-1]

In Formula 1-1,

R1 is as defined in Formula 1 above.

In one embodiment of the present invention, R1 in Formula 1 may be a straight-chain or branched alkylene group having 1 to 3 carbon atoms, preferably a straight-chain alkylene group having 1 to 3 carbon atoms, more preferably a methylene group. You can.

As a preferred example, the first additive may be represented by the following formula 1A.

[Formula 1A]

In one embodiment of the present invention, the content of the first additive is 0.05% by weight to 10% by weight, preferably 0.1% by weight to 1% by weight, more preferably 0.1% by weight, based on the total weight of the non-aqueous electrolyte solution. It may be from 0.5% by weight. Considering that if the content of the first additive is excessive, it participates excessively in the decomposition reaction at the interface between the electrode and the electrolyte solution, and the film resistance becomes excessively large, which may cause a problem of increasing the resistance of the battery, the content of the first additive It is preferable that silver is 10% by weight or less.

Additionally, the non-aqueous electrolyte solution of the present invention includes a second additive represented by the following formula (2).

[Formula 2]

In Formula 2,

R2 is an alkyl group having 1 to 10 carbon atoms substituted with one or more fluorines.

Since the second additive represented by Formula 2 contains a cyclic phosphate structure, when it is included in the electrolyte solution, an SEI film of polyphosphoester (PPE) component can be formed on the cathode surface through a ring opening reaction, which Elasticity can be imparted to the silicon anode. In other words, the durability of silicon against volume changes is strengthened, so deterioration of the cathode can be prevented in cycling and high-temperature environments. In addition, since the second additive contains a fluoroalkyl group, it can form a LiF-based inorganic SEI film on the anode and cathode through reaction with lithium ions. LiF has physically strong properties and a strong bond with lithiated silicon (Li _x Si), so it has the effect of suppressing battery deterioration due to reaction at the electrolyte and electrode interface.

In one embodiment of the present invention, R2 in Formula 2 is -(CR ₂ ) _n CF ₃ , R is hydrogen or fluorine, and n may be an integer from 0 to 9. Preferably, R2 in Formula 2 is -(CH ₂ ) _n CF ₃ , n may be an integer of 0 to 5, and more preferably, n may be an integer of 1 to 3.

As a preferred example, the second additive may be represented by the following formula 2A.

[Formula 2A]

In one embodiment of the present invention, the content of the second additive may be 0.1% by weight to 15% by weight based on the total weight of the non-aqueous electrolyte solution.

Specifically, the content of the second additive may be 0.5% by weight or more, preferably 2% by weight or more, more preferably 5% by weight or more, and most preferably 10% by weight or more based on the total weight of the non-aqueous electrolyte solution. . However, considering that if the second additive is excessively added, the resistance of the battery may increase due to decomposition, the content of the second additive is preferably 15% by weight or less.

In the non-aqueous electrolyte solution according to the present invention, when the first additive and the second additive are used together, the A substituent of Formula 1, specifically the lone electron pair present in imidazole, is used in the formula 2 of the second additive. By further promoting the ring-opening reaction, the reduction reaction can occur smoothly with less energy. As a result, the polymerized film component can be further increased when forming the SEI layer on the silicon anode, and the generation of HF can be suppressed by chelating PF ₅ . In particular, in the case of Si anode materials, the change in volume is large, so film damage and durability deterioration caused by HF intensify in a high temperature environment, so the effect of improving durability and reducing gas generation can be more dramatic through the combination of these additives.

In one embodiment of the present invention, the weight ratio of the second additive to the first additive, that is, the ratio of the weight (W2) of the second additive to the weight (W1) of the first additive in the non-aqueous electrolyte solution (W2/ W1) may be 1.5 or more, preferably 6 or more, more preferably 16 or more, and most preferably 30 or more. As the relative ratio of the second additive increases, the formation of a polymerized film due to the ring-opening reaction of the cyclic phosphate structure is not only advantageous, but also the LiF formed by the combination of -CF ₃ and lithium ions plays a role in strengthening the durability of the film. Therefore, it is desirable to improve the high-temperature performance of batteries using Pure Si as an anode material. However, when the film of the polymer component is formed too thick due to excessive decomposition of the additive, battery resistance increases, and considering that side reactions and by-products are caused during the decomposition process, the weight ratio of the second additive to the first additive is 40 or less. It is desirable.

(2) Third additive

The non-aqueous electrolyte is a third additive selected from the group consisting of cyclic carbonate-based compounds, sultone-based compounds, sulfate-based compounds, phosphorus-based compounds, nitrile-based compounds, amine-based compounds, silane-based compounds, benzene-based compounds, and lithium salt-based compounds. It may contain the above compounds.

The cyclic carbonate-based compound may be one or more selected from the group consisting of vinylene carbonate (VC), vinyl ethylene carbonate (VEC), and fluoroethylene carbonate (FEC), and may specifically be vinylene carbonate.

The sultone-based compound is a material that can form a stable SEI film through a reduction reaction on the cathode surface, and includes 1,3-propane sultone (PS), 1,4-butane sultone, ethenesultone, and 1,3-propene sultone ( PRS), 1,4-butene sultone, and 1-methyl-1,3-propene sultone. It may be one or more selected from the group consisting of 1,3-propane sultone (PS).

The sulfate-based compound is a material that can be electrically decomposed on the surface of the cathode to form a stable SEI film that does not crack even when stored at high temperatures, and includes ethylene sulfate (Esa), trimethylene sulfate (TMS), and methyltrimethylene sulfate. It may be one or more selected from the group consisting of methylene sulfate (Methyl trimethylene sulfate; MTMS).

The phosphorus-based compound may be a phosphate-based or phosphite-based compound, and specifically, tris(trimethylsilyl)phosphate, tris(trimethylsilyl)phosphate, and tris(2,2,2-trifluoroethyl)phosphate. and tris(trifluoroethyl)phosphite.

The nitrile-based compounds include succinonitrile (SN), adiponitrile (ADN), acetonitrile, propionitrile, butyronitrile, valeronitrile, caprylonitrile, heptanenitrile, cyclopentane carbonitrile, and cyclohexane carbonitrile. , 2-fluorobenzonitrile, 4-fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile, phenylacetonitrile, 2-fluorophenylacetonitrile, 4-fluorophenylacetonitrile, ethylene glycol bis. (2-cyanoethyl) ether (ASA3), 1,3,6-hexane tricarbonitrile (HTCN), 1,4-dicyano 2-butene (DCB) and 1,2,3-tris (2- It may be one or more selected from the group consisting of cyanoethyl) propane (TCEP).

The amine-based compound may be at least one selected from the group consisting of triethanolamine and ethylenediamine, and the silane-based compound may be tetravinylsilane.

The benzene-based compound may be any one or more selected from the group consisting of monofluorobenzene, difluorobenzene, trifluorobenzene, and tetrafluorobenzene.

The lithium salt-based compound is a compound different from the lithium salt contained in the non-aqueous electrolyte solution, and includes lithium difluorophosphate (LiDFP; LiPO ₂ F ₂ ), lithium bisoxalate borate (LiBOB; LiB(C ₂ O ₄ ) ₂ ), It may be any one or more selected from the group consisting of lithium tetrafluoroborate (LiBF ₄ ), lithium tetraphenylborate, and lithium difluoro(bisoxalato)phosphate (LiDFOP).

Preferably, the non-aqueous electrolyte according to an embodiment of the present invention includes vinylene carbonate (VC), 1,3-propane sultone (PS), 1,3-propene sultone (PRS), and lithium difluorophosphate (LiDFP). ) may further include one or more third additives selected from the group consisting of In this case, a more robust SEI layer can be formed on the surface of the cathode during the initial activation process of the secondary battery, thereby suppressing gas generation due to decomposition of the electrolyte at high temperatures and lowering the rate of increase in resistance due to increased cycles during battery operation.

In one embodiment of the present invention, the content of the third additive may be 0.05% by weight to 5% by weight, preferably 0.1% by weight to 3% by weight, based on the total weight of the non-aqueous electrolyte solution. It is preferable that the content of the third additive is 5% by weight or less in terms of lowering the initial resistance.

(3) Organic solvent

The non-aqueous electrolyte solution of the present invention contains an organic solvent.

As the organic solvent, various organic solvents commonly used in lithium electrolytes can be used without limitation. For example, the organic solvent may be a cyclic carbonate-based solvent, a linear carbonate-based solvent, a linear ester-based solvent, a cyclic ester-based solvent, a nitrile-based solvent, or a mixture thereof, and preferably a cyclic carbonate-based solvent and a linear carbonate-based solvent. It may include a mixture of solvents, and more preferably, it may be a mixture of a fluorinated cyclic carbonate-based solvent and a linear carbonate-based solvent.

The cyclic carbonate-based solvent is a high-viscosity organic solvent that has a high dielectric constant and can easily dissociate lithium salts in the electrolyte. It can be used in ethylene carbonate (EC), propylene carbonate (PC), fluoroethylene carbonate (FEC), and 1,2-butyl. It may be at least one selected from the group consisting of lene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 2,3-pentylene carbonate and vinylene carbonate, preferably fluoroethylene carbonate. (FEC) may be included. When using a fluorinated cyclic carbonate-based solvent such as FEC, a LiF-based inorganic SEI layer can be formed, so there is an advantage in that a hybrid film can be formed together with the organic film of the polymer component formed by the additive.

In addition, the linear carbonate-based solvent is an organic solvent having low viscosity and low dielectric constant, such as dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, ethylmethyl carbonate (EMC), and methyl carbonate. It may be any one or more selected from the group consisting of propyl carbonate and ethylpropyl carbonate, and may preferably include diethyl carbonate (DEC), ethylmethyl carbonate (EMC), or a mixture thereof, and more preferably diethyl carbonate. carbonate and ethylmethyl carbonate. DMC is an organic solvent that is effective in increasing ionic conductivity and thereby improving room temperature resistance. However, when DMC is used alone as the linear carbonate-based solvent, it is unstable at high temperatures, resulting in increased gas formation due to reduction reactions, and its high freezing point at low temperatures. It has the disadvantage of significantly reducing performance. Therefore, it is desirable to reduce the amount of gas generated, enhance the durability of the film formed on the electrode, and improve the low-temperature performance of the battery by using DEC, EMC, or a combination thereof. In particular, EMC has a lower viscosity than DEC, so it is advantageous in improving ionic conductivity.

The linear ester solvent may be at least one selected from the group consisting of methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, and butyl propionate, and is preferably methyl propionate. It may be propionate, ethyl propionate or propyl propionate.

The cyclic ester-based solvent may be one or more selected from the group consisting of γ-butyrolactone, γ-valerolactone, γ-caprolactone, σ-valerolactone, and ε-caprolactone.

The nitrile-based solvents include succinonitrile, acetonitrile, propionitrile, butyronitrile, valeronitrile, caprylonitrile, heptanenitrile, cyclopentane carbonitrile, cyclohexane carbonitrile, 2-fluorobenzonitrile, 4- It may be at least one selected from the group consisting of fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile, phenylacetonitrile, 2-fluorophenylacetonitrile, and 4-fluorophenylacetonitrile, preferably It may be succinonitrile.

Of the total weight of the non-aqueous electrolyte, the remainder excluding the content of other components excluding the organic solvent, such as the first to third additives and lithium salt, may be organic solvents unless otherwise specified.

(4) Lithium salt

The non-aqueous electrolyte solution of the present invention contains lithium salt.

The lithium salt may be those commonly used in electrolytes for lithium secondary batteries without limitation. Specifically, the lithium salt includes Li ⁺ as a cation, and F ^- , Cl ^- , Br ^- , I ^- , NO as an anion. ₃ ^- , N(CN) ₂ ^- , BF ₄ ^- , ClO ₄ ^- , B ₁₀ Cl ₁₀ ^- , AlCl ₄ ^- , AlO ₄ ^- , PF ₆ ^- , CF ₃ SO ₃ ^- , CH ₃ CO ₂ ^- , CF ₃ CO ₂ ^- , AsF ₆ ^- , SbF ₆ ^- , CH ₃ SO ₃ ^- , (CF ₃ CF ₂ SO ₂ ) ₂ N ^- , (CF ₃ SO ₂ ) ₂ N ^- , (FSO ₂ ) ₂ N ^- , BF ₂ C ₂ O ₄ ^- , BC ₄ O ₈ ^- , BF ₂ C ₂ O ₄ CHF-, PF ₄ C ₂ O ₄ ^- , PF ₂ C ₄ O ₈ ^- , PO ₂ F ₂ ^- , (CF ₃ ) ₂ PF ₄ ^- , (CF ₃ ) ₃ PF ₃ ^- , (CF ₃ ) ₄ PF ₂ ^- , (CF ₃ ) ₅ PF ^- , (CF ₃ ) ₆ P ^- , C ₄ F ₉ SO ₃ ^- , CF ₃ CF ₂ SO ₃ ^- , CF ₃ CF ₂ (CF ₃ ) ₂ CO ^- , (CF ₃ SO ₂ ) ₂ CH ^- , CF ₃ (CF ₂ ) ₇ SO ₃ ^- and SCN ^- may include any one or more selected from these.

Specifically, the lithium salt is LiPF ₆ , LiClO ₄ , LiBF ₄ , LiN(FSO ₂ ) ₂ (LiFSI), LiTFSI, lithium bis(pentafluoroethanesulfonyl)imide (LiBETI) , LiSO ₃ CF ₃ , LiPO ₂ F ₂ , Lithium bis(oxalate)borate (LiBOB), Lithium difluoro(oxalate)borate (LiFOB), Lithium Lithium difluoro(bisoxalato) phosphate, LiDFOP, Lithium tetrafluoro(oxalate) phosphate, LiTFOP, and Lithium fluoromalonato ) It may be one or more selected from the group consisting of borate (Lithium fluoromalonato(difluoro) borate, LiFMDFB), preferably LiPF ₆ .

In one embodiment of the present invention, the concentration of the lithium salt in the non-aqueous organic solution containing the lithium salt and the organic solvent, that is, the mixed solution of the lithium salt and the organic solvent, is 0.5M or more, specifically 1.0M or more, more specifically It can be more than 1.5M. When the concentration of lithium salt is in the above range, low-temperature output improvement and cycle characteristics improvement effects can be sufficiently secured. In particular, when the concentration of lithium salt is higher than 1.5M, anion participates in the lithium ion solvation shell in the electrolyte phase. The degree may increase. Accordingly, inorganic components such as LiF are added to the anode SEI layer by anions in the lithium salt, such as PF ₆ ^- , thereby enhancing the durability of the silicon anode against volume changes. Meanwhile, in order to prevent excessive increase in viscosity and surface tension and obtain appropriate electrolyte impregnability, it is preferable that the concentration of the lithium salt is 4.0M or less, specifically 3.0M or less, and more specifically 2.0M or less.

anode

The positive electrode according to the present invention contains a positive electrode active material, and can be manufactured by coating a positive electrode slurry containing a positive electrode active material, a binder, a conductive material, and a solvent on a positive electrode current collector, followed by drying and rolling.

The positive electrode current collector is not particularly limited as long as it has conductivity without causing chemical changes in the battery. For example, stainless steel; aluminum; nickel; titanium; calcined carbon; Alternatively, the surface of aluminum or stainless steel may be treated with carbon, nickel, titanium, silver, etc.

The positive electrode active material is a compound capable of reversible intercalation and deintercalation of lithium, including LCO (LiCoO ₂ ); LNO(LiNiO ₂ ); LMO(LiMnO ₂ ); LiMn ₂ O ₄ , LiCoPO ₄ ; LFP(LiFePO ₄ ); and lithium complex transition metal oxides containing nickel (Ni), cobalt (Co), and manganese (Mn).

Meanwhile, the positive electrode active material may be a lithium composite transition metal oxide in which the molar ratio of nickel in the transition metal is 70 mol% or more, preferably 80 mol% or more, and more preferably 85 mol% or more.

In the case of a high-Ni positive electrode active material with a nickel content of 70 mol% or more out of the total transition metal content, it is structurally unstable, so collapse and cracking of the positive electrode active material may occur at high temperatures. In the case of an active material that collapses in this way, the surface area increases, increasing the number of sites where side reactions with the electrolyte can occur, and this causes a large amount of gas to be generated when exposed to high temperatures. If gas is continuously generated like this, the internal pressure of the battery increases, causing a vent to occur early and stopping the operation before the battery reaches the end of its lifespan. Therefore, it is important to improve these side reactions and gas generation. This can be improved by strengthening film formation through a non-aqueous electrolyte solution containing the first and second additives of the present invention.

In one embodiment of the present invention, the lithium complex transition metal oxide may be a compound represented by the following formula (3). That is, the positive electrode active material according to an exemplary embodiment of the present invention may include a lithium complex transition metal oxide represented by the following formula (3).

[Formula 3]

Li _1+x (Ni _a Co _b Mn _c M _d )O ₂

In Formula 3 above,

M is W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B and Mo. It is one or more selected from the group consisting of

1+x, a, b, c and d are the atomic fractions of each independent element,

-0.2≤x≤0.2, 0.60≤a<1, 0<b≤0.30, 0<c≤0.30, 0≤d≤0.10, a+b+c+d=1.

The 1+x represents the molar ratio of lithium in the lithium composite transition metal oxide and may be -0.1≤x≤0.2, or 0≤x≤0.2. When the molar ratio of lithium satisfies the above range, the crystal structure of the lithium composite transition metal oxide can be stably formed.

The a represents the molar ratio of nickel to all metals excluding lithium in the lithium composite transition metal oxide, and may be 0.70≤a<1, 0.80≤a<1, or 0.85≤a<1. When the molar ratio of nickel satisfies the above range, high energy density is exhibited, making it possible to implement high capacity.

The b represents the molar ratio of cobalt to all metals excluding lithium in the lithium composite transition metal oxide, and may be 0<b≤0.20, 0<b≤0.15, or 0<b≤0.10. When the molar ratio of cobalt satisfies the above range, good resistance characteristics and output characteristics can be achieved.

The c represents the molar ratio of manganese to all metals excluding lithium in the lithium composite transition metal oxide, and may be 0<c≤0.20, 0<c≤0.15, or 0<c≤0.10. When the molar ratio of manganese satisfies the above range, the structural stability of the positive electrode active material is excellent.

In one embodiment of the present invention, the lithium composite transition metal oxide is W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, It may contain one or more doping elements selected from the group consisting of Sm, Ca, Ce, Nb, Mg, B, and Mo, and may preferably contain Al as the doping element. In other words, d, which represents the molar ratio of doping elements among all metals excluding lithium in the lithium composite transition metal oxide, may be 0<d≤0.10, 0<d≤0.08, or 0<d≤0.05.

Preferably, a, b, c, and d in Formula 3 may be 0.70≤a<1, 0<b≤0.20, 0<c≤0.20, and 0≤d≤0.10, respectively.

The positive electrode active material may be included in an amount of 80% to 99% by weight, specifically 90% to 99% by weight, based on the total weight of solids in the positive electrode slurry. At this time, if the content of the positive electrode active material is 80% by weight or less, the energy density may be lowered and the capacity may be reduced.

The binder is a component that assists the bonding of the active material and the conductive material and the bonding to the current collector, and can typically be added in an amount of 1% to 30% by weight based on the total weight of solids in the positive electrode slurry. Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, and polytetrafluoroethylene. , polyethylene, polypropylene, ethylene-propylene-diene monomer, sulfonated ethylene-propylene-diene monomer, styrene-butadiene rubber, fluorine rubber, or various copolymers thereof.

Additionally, the conductive material is a material that provides conductivity without causing chemical changes in the battery, and may be added in an amount of 0.5% to 20% by weight based on the total weight of solids in the positive electrode slurry.

The conductive material includes, for example, carbon black such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black; Graphite powders such as natural graphite, artificial graphite, carbon nanotubes, and graphite; Conductive fibers such as carbon fiber and metal fiber; Conductive powders such as fluorinated carbon powder, aluminum powder, and nickel powder; Conductive whiskers such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives.

In addition, the solvent of the positive electrode slurry may include an organic solvent such as NMP (N-methyl-2-pyrrolidone), and can be used in an amount that achieves a desirable viscosity when including the positive electrode active material, binder, and conductive material. . For example, the solid content concentration in the positive electrode slurry including the positive electrode active material, binder, and conductive material may be 40% by weight to 90% by weight, preferably 50% by weight to 80% by weight.

cathode

The lithium secondary battery according to the present invention includes a negative electrode containing a negative electrode active material, and the negative electrode is formed by coating a negative electrode slurry containing a negative electrode active material, a binder, a conductive material, and a solvent on a negative electrode current collector, followed by drying and rolling. It can be manufactured.

The negative electrode current collector generally has a thickness of 3㎛ to 500㎛. This negative electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery. For example, copper; stainless steel; aluminum; nickel; titanium; calcined carbon; Surface treatment of copper or stainless steel with carbon, nickel, titanium, silver, etc.; Alternatively, an aluminum-cadmium alloy, etc. may be used. In addition, like the positive electrode current collector, the bonding power of the negative electrode active material can be strengthened by forming fine irregularities on the surface, and can be used in various forms such as films, sheets, foils, nets, porous materials, foams, and non-woven materials.

In the present invention, the negative electrode active material is made of silicon (Si). As a negative electrode active material, silicon has a theoretical capacity that is approximately 10 times higher than that of graphite, which not only makes it possible to implement a high-capacity cell, but also improves the rapid charging performance of the battery by lowering the mass loading (mg·cm ^-2 ). However, there is a problem that the lithium ion loss rate due to an irreversible reaction is high and the volume change is large, which can adversely affect the lifespan. In particular, in the case of 100% Si cathode, the SEI film is easily broken and regenerated due to large volume changes during the charging and discharging process. As the reaction continues to occur, the phenomenon becomes more severe. However, when applying the non-aqueous electrolyte according to the present invention, the SEI film can be strengthened as described above, so this problem can be effectively solved.

The negative electrode active material may be included in an amount of 60% to 99% by weight based on the total weight of solids in the negative electrode slurry.

The binder is a component that assists in bonding between the conductive material, the active material, and the current collector, and can typically be added in an amount of 1% to 30% by weight based on the total weight of solids in the negative electrode slurry. Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, and polytetrafluoroethylene. , polyethylene, polypropylene, ethylene-propylene-diene monomer, sulfonated ethylene-propylene-diene monomer, styrene-butadiene rubber, fluorine rubber, or various copolymers thereof.

The conductive material is a component to further improve the conductivity of the negative electrode active material, and may be added in an amount of 0.5% to 20% by weight based on the total weight of solids in the negative electrode slurry. These conductive materials are not particularly limited as long as they have conductivity without causing chemical changes in the battery, and include, for example, carbon black such as acetylene black, Ketjen black, channel black, furnace black, lamp black, or thermal black; Graphite powder with a highly developed crystal structure, such as natural graphite, artificial graphite, carbon nanotubes, or graphite; Conductive fibers such as carbon fibers or metal fibers; Conductive powders such as fluorinated carbon powder, aluminum powder, or nickel powder; Conductive whiskers such as zinc oxide or potassium titanate; Conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives; Or a combination thereof may be used.

The solvent of the cathode slurry is water; Alternatively, it may contain an organic solvent such as NMP and alcohol, and may be used in an amount that provides a desirable viscosity when including the negative electrode active material, binder, and conductive material. For example, the solid content concentration in the slurry containing the negative electrode active material, binder, and conductive material may be 20% by weight to 80% by weight, preferably 20% by weight to 40% by weight.

separator

The lithium secondary battery according to the present invention includes a separator between the positive electrode and the negative electrode.

The separator separates the cathode from the anode and provides a passage for lithium ions to move. It can be used without particular restrictions as long as it is normally used as a separator in lithium secondary batteries. In particular, it has low resistance to ion movement in the electrolyte and has an electrolyte impregnation ability. It is desirable that it is excellent and has excellent safety.

Specifically, a porous polymer film as a separator, for example, a porous polymer film made of polyolefin polymers such as ethylene homopolymer, propylene homopolymer, ethylene/butene copolymer, ethylene/hexene copolymer, and ethylene/methacrylate copolymer. ; Alternatively, a laminated structure of two or more layers thereof may be used. In addition, conventional porous non-woven fabrics, for example, non-woven fabrics made of high melting point glass fibers, polyethylene terephthalate fibers, etc., may be used. Additionally, a coated separator containing ceramic components or polymer materials may be used to ensure heat resistance or mechanical strength, and may be used in a single-layer or multi-layer structure.

The lithium secondary battery according to the present invention as described above can be used in portable devices such as mobile phones, laptop computers, and digital cameras; And it can be usefully used in the field of electric vehicles such as hybrid electric vehicles (HEV).

Accordingly, according to another embodiment of the present invention, a battery module including the lithium secondary battery as a unit cell and a battery pack including the same are provided.

The battery module or battery pack is a power tool; Electric vehicles, including electric vehicles (EV), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEV); and a power storage system. It can be used as a power source for one or more mid- to large-sized devices.

The external shape of the lithium secondary battery of the present invention is not particularly limited, but may be cylindrical, prismatic, pouch-shaped, or coin-shaped using a can.

The lithium secondary battery according to the present invention can not only be used in battery cells used as a power source for small devices, but can also be preferably used as a unit cell in medium to large-sized battery modules containing a plurality of battery cells.

Hereinafter, the present invention will be described in detail through specific examples.

<Example>

Example 1.

(Preparation of non-aqueous electrolyte solution)

A non-aqueous organic solution was prepared by mixing fluoroethylene carbonate (FEC):diethyl carbonate (DEC):ethylmethyl carbonate (EMC) in a volume ratio of 10:45:45 and then dissolving LiPF ₆ to 1.5M. . 100 wt% non-aqueous electrolyte solution was prepared by mixing 0.3 wt% of the compound represented by Formula 1A, 0.5 wt% of the compound represented by Formula 2A, and the remainder of the non-aqueous organic solution.

(Manufacture of lithium secondary batteries)

Li(Ni _0.85 Co _0.05 Mn _0.08 Al _0.02 )O ₂ as the positive electrode active material, carbon black as the conductive material, polyvinylidene fluoride as the binder, and N-methyl-2-pyrrolidone as the solvent at a weight ratio of 97.74:0.7:1.56. (NMP) was added to prepare a positive electrode slurry (solid content: 75.5% by weight). The positive electrode slurry was applied to a positive electrode current collector (Al thin film) with a thickness of 15㎛, and dried and roll pressed to prepare a positive electrode.

Distilled water as a solvent was mixed with Si particles with an average particle diameter of 5㎛ (Wacker) as a negative electrode active material, styrene-butadiene rubber-carboxymethylcellulose (SBR-CMC) as a binder, and carbon black as a conductive material at a ratio of 70:9.7:20.3. A negative electrode active material slurry with a solid content of 26.0% by weight was prepared by mixing in a weight ratio. The negative electrode active material slurry was applied to a negative electrode current collector (Cu thin film) with a thickness of 15㎛, and dried and roll pressed to prepare a negative electrode.

An electrode assembly was manufactured by sequentially stacking the anode, a polyolefin-based porous separator coated with inorganic particles (Al ₂ O ₃ ), and a cathode.

The assembled electrode assembly was stored in a pouch-type battery case, and the prepared non-aqueous electrolyte solution was injected to manufacture a lithium secondary battery.

Example 2.

A lithium secondary battery was manufactured in the same manner as in Example 1, except that the content of the compound represented by Chemical Formula 2A was changed to 2 wt% when preparing the non-aqueous electrolyte solution.

Example 3.

A lithium secondary battery was manufactured in the same manner as Example 1, except that the content of the compound represented by Chemical Formula 2A was changed to 5 wt% when preparing the non-aqueous electrolyte solution.

Example 4.

A lithium secondary battery was manufactured in the same manner as in Example 1, except that the content of the compound represented by Chemical Formula 2A was changed to 10 wt% when preparing the non-aqueous electrolyte solution.

Example 5.

A lithium secondary battery was manufactured in the same manner as in Example 1, except that the content of the compound represented by Formula 1A was changed to 10 wt% when preparing the non-aqueous electrolyte solution.

Example 6.

A lithium secondary battery was manufactured in the same manner as Example 1, except that 2.5 wt% of vinylene carbonate (VC) was added when preparing the non-aqueous electrolyte solution.

Comparative Example 1.

A lithium secondary battery was manufactured in the same manner as in Example 1, except that the compound represented by Formula 1A and the compound represented by Formula 2A were not added when preparing the non-aqueous electrolyte solution.

Comparative Example 2.

A lithium secondary battery was manufactured in the same manner as Example 1, except that the compound represented by Chemical Formula 2A was not added when preparing the non-aqueous electrolyte solution.

Comparative Example 3.

A lithium secondary battery was manufactured in the same manner as Example 1, except that the compound represented by Formula 1A was not added when preparing the non-aqueous electrolyte solution.

Comparative Example 4.

A lithium secondary battery was manufactured in the same manner as in Example 1, except that a compound represented by the following formula Z1 (5-Ethynyl-1-methyl-1H-imidazole) was used instead of the compound represented by the formula 1A when preparing the non-aqueous electrolyte solution. was manufactured.

[Formula Z1]

Comparative Example 5.

When preparing the non-aqueous electrolyte, the same method as Example 1 was used, except that a compound represented by the following formula Z2 (2-Ethoxy-1,3,2-dioxaphospholane 2-Oxide) was used instead of the compound represented by the formula 2A. A lithium secondary battery was manufactured.

[Formula Z2]

Comparative Example 6-1.

Instead of the slurry described in Example 1 as the negative electrode active material slurry, a mixture of SiO and artificial graphite as a negative electrode active material blended at a weight ratio of 2:8 in distilled water as a solvent, and styrene-butadiene rubber-carboxymethylcellulose (SBR-) as a binder were used. A lithium secondary battery was prepared in the same manner as in Example 1, except that a mixture of CMC), carbon black as a conductive material, and sodium carboxymethyl cellulose (CMC) as a thickener at a weight ratio of 96.0:2.3:0.7:1 was used. was manufactured.

Comparative Example 6-2.

A lithium secondary battery was manufactured in the same manner as Comparative Example 6-1, except that the compound represented by Chemical Formula 2A was not added when preparing the non-aqueous electrolyte solution.

Comparative Example 6-3.

A lithium secondary battery was manufactured in the same manner as Comparative Example 6-1, except that the compound represented by Chemical Formula 1A was not added when preparing the non-aqueous electrolyte solution.

<Experimental example>

Experimental Example 1: Evaluation of gas generation after high temperature (45°C) cycle

An activation (formation) process was performed on the lithium secondary batteries manufactured in Examples 1 to 6 and Comparative Examples 1 to 5 and 6-1 to 6-3, and then constant current/constant voltage up to 4.2V at 1C rate at 45°C. (CC/CV) charging (0.05C cut off) was performed, and constant current (CC) discharge was performed up to 3.0V at a 0.5C rate.

In addition, after 200 cycles, the charged battery was moved to a charger and discharger at room temperature (25°C), and then the gas collected in the pouch was analyzed using GC-TCD (gas chromatography-thermal conductivity detector), and the When the gas generation amount was set to 100%, the relative gas generation amount of each battery was calculated and listed in Table 1 below.

Experimental Example 2: Evaluation of gas generation after storage at high temperature (60°C)

An activation (formation) process was performed on the lithium secondary batteries manufactured in Examples 1 to 6 and Comparative Examples 1 to 5 and 6-1 to 6-3, and then subjected to a constant current up to 4.2V at a rate of 0.33C at 25°C. Charging was performed under constant voltage conditions (0.05C cut off) and fully charged to SOC 100%. The fully charged battery was stored at 60°C for 8 weeks, then transferred to a charger and discharger at room temperature (25°C), and the gas collected in the pouch was analyzed using GC-TCD (gas chromatography-thermal conductivity detector). Comparative Example 1 When the measured gas generation amount was set to 100%, the relative gas generation amount of each battery was calculated and listed in Table 1 below.

negative active material first additive second additive third additive Experimental Example 1 Experimental Example 2 chemical formula content
(wt%) chemical formula content
(wt%) chemical formula content
(wt%) Gas generation (%) Gas generation (%) Example 1 Pure Si 1A 0.3 2A 0.5 - - 80.4 85.4 Example 2 Pure Si 1A 0.3 2A 2 - - 74.5 79.2 Example 3 Pure Si 1A 0.3 2A 5 - - 41.9 48.5 Example 4 Pure Si 1A 0.3 2A 10 - - 33.5 39.4 Example 5 Pure Si 1A 10 2A 0.3 - - 70.8 73.5 Example 6 Pure Si 1A 0.3 2A 0.5 VC 2.5 87.8 89.0 Comparative Example 1 Pure Si - - - - - - 100 100 Comparative Example 2 Pure Si 1A 0.3 - - - - 98.7 95.7 Comparative Example 3 Pure Si - - 2A 0.5 - - 97.4 92.5 Comparative Example 4 Pure Si Z1 0.3 2A 0.5 - - 99.5 98.9 Comparative Example 5 Pure Si 1A 0.3 Z2 0.5 - - 112.1 105.8 Comparative Example 6-1 SiO+C 1A 0.3 2A 0.5 - - 95.7 93.8 Comparative Example 6-2 SiO+C 1A 0.3 - - - - 99.8 98.3 Comparative Example 6-3 SiO+C - - 2A 0.5 - - 99.2 97.1

Through the results in Table 1, when the first additive and the second additive of the present application are simultaneously included as electrolyte additives, the amount of gas generated after high temperature cycling and high temperature storage of a lithium secondary battery using 100 wt% of Si as a negative electrode active material is reduced. You can see what is effective.

Specifically, when only the first additive or the second additive is used alone (Comparative Examples 2 and 3), compared to the case where neither the first additive nor the second additive is included (Comparative Example 1), the effect of reducing the amount of gas generated is You can see that it is very slight. In addition, the compound of formula Z1 used in Comparative Example 4 is a propargyl-substituted imadisole compound, but it can be seen that the effect of reducing gas generation is significantly reduced when used instead of the first additive of the present application. Moreover, the compound of Chemical Formula Z2 used in Comparative Example 5 is a cyclic phosphate compound like the second additive of the present application, but since a methyl group rather than a fluoroalkyl group is located at the terminal (R2 of Chemical Formula 2), the increase in film resistance is rather severe, resulting in an increase in gas generation. It can be seen that there is a further increase compared to Comparative Example 1 in which no additives were used. This is a phenomenon that occurs because, in the case of fluoroalkyl, components with excellent durability and ion conductivity, such as LiF, contribute to being included in the SEI layer, but methyl groups only produce polyolefin components that are not conductive and have poor durability. In other words, a part of the SEI layer cannot withstand the volume expansion of the Si cathode and is lost, and as the cycle progresses, another film is continuously created in the lost part due to a side reaction of the electrolyte, which intensifies the increase in film resistance.

On the other hand, in the case of Comparative Example 6-1, which used a mixture of SiO and graphite instead of Si as the negative electrode active material, not only was the amount of gas generated more than that of Example 1, but also the first additive and the second additive were used alone. When compared to 2 and 6-3, it can be seen that the effect of reducing gas generation is minimal. Through Comparative Examples 6-1 to 6-3, it can be seen that the combination of the first and second additives of the present invention shows a particularly significant effect in improving the amount of high-temperature gas generation in a battery containing a Pure Si negative electrode active material.

In addition, among Examples 1 to 6, it can be seen that Examples 3 and 4, in which the weight ratio (W2/W1) of the second additive to the first additive is 15 or more, have the most excellent gas generation reduction effect.

Experimental Example 3: Evaluation of capacity retention rate after high temperature (45°C) cycle

An activation (formation) process was performed on the lithium secondary batteries prepared in Examples 1 to 6 and Comparative Examples 1 to 5, and then constant current/constant voltage (CC/CV) charging (0.05C) up to 4.2V at 1C rate at 45°C. cut off) was performed, and constant current (CC) discharge was performed up to 3.0V at a rate of 0.5C.

Performing the above charge/discharge once each was regarded as 1 cycle, and the same charge/discharge was repeated 200 times. The capacity maintenance rate after 200 cycles was measured compared to the initial discharge capacity after 1 cycle, and the results are listed in Table 2 below.

negative active material first additive second additive third additive Experimental Example 3 chemical formula content
(wt%) chemical formula content
(wt%) chemical formula content
(wt%) Capacity maintenance rate (%) Example 1 Pure Si 1A 0.3 2A 0.5 - - 84.5 Example 2 Pure Si 1A 0.3 2A 2 - - 86.8 Example 3 Pure Si 1A 0.3 2A 5 - - 89.2 Example 4 Pure Si 1A 0.3 2A 10 - - 93.5 Example 5 Pure Si 1A 10 2A 0.3 - - 87.5 Example 6 Pure Si 1A 0.3 2A 0.5 VC 2.5 85.8 Comparative Example 1 Pure Si - - - - - - 75.2 Comparative Example 2 Pure Si 1A 0.3 - - - - 77.6 Comparative Example 3 Pure Si - - 2A 0.5 - - 79.4 Comparative Example 4 Pure Si Z1 0.3 2A 0.5 - - 65.8 Comparative Example 5 Pure Si 1A 0.3 Z2 0.5 - - 60.1

Through the results in Table 1, it can be confirmed that when the first and second additives of the present application are simultaneously included as electrolyte additives, it is effective in improving the high temperature lifespan of a lithium secondary battery using 100 wt% of Si as a negative electrode active material.

Specifically, the capacity retention rate is significantly higher not only when neither the first nor the second additive is included (Comparative Example 1), but also when compared to when only the first or second additive is used alone (Comparative Examples 2 and 3). You can see the improvement. In addition, the compound of formula Z1 used in Comparative Example 4 and the compound of formula Z2 used in Comparative Example 5 have similar structures to the first and second additives of the present invention, respectively, but actually worsen the lifespan characteristics. You can check that.

Meanwhile, among Examples 1 to 6, it can be seen that Examples 3 and 4, in which the weight ratio (W2/W1) of the second additive to the first additive is 15 or more, have the most excellent capacity retention rate improvement effect.

Experimental Example 4: Rapid charging performance evaluation

For each lithium secondary battery manufactured in Examples 1 to 6 and Comparative Examples 1 to 5 and 6-1 to 6-3, a formation process was performed, and then the battery was heated to 4.2V at a 1C rate at 25°C. Constant current/constant voltage (CC/CV) charging (0.05C cut off) was performed, constant current (CC) discharge was performed up to 3.0V at a 0.5C rate, and initial discharge capacity, initial resistance, and initial volume were measured. At this time, the volume was measured using the buoyancy method.

Next, after adjusting the lithium secondary battery to SOC (State Of Charge) 15%, charging is performed at 25°C while changing the C-rate according to the SOC state as shown in Table 3 below, and 1 charge is charged for each charging section. The voltage profile was measured by checking the voltage value at intervals of seconds.

Charging time (sec) C-rate(C) SOC 15%~95% 720 4.0

Afterwards, the termination conditions were set using the voltage values for each section obtained in each section, and the charging amount when charged in CC mode was recorded. Then, it was discharged again in CC mode at 0.33C to SOC 15%.

After performing 100 cycles by considering the charging and discharging as 1 cycle, the capacity retention rate, resistance increase rate, and volume increase rate were calculated according to Equations 1 to 3 below and are listed in Table 4 below.

[Equation 1]

Capacity maintenance rate (%) = (discharge capacity after 100 cycles/initial discharge capacity) × 100

[Equation 2]

Resistance increase rate (%) = {(resistance after 100 cycles - initial resistance)/initial resistance} × 100

[Equation 3]

Volume increase rate (%) = {(Volume after 100 cycles - Initial volume)/Initial volume} × 100

negative active material first additive second additive third additive Experimental Example 4 chemical formula content
(wt%) chemical formula content
(wt%) chemical formula content
(wt%) Capacity maintenance rate (%) resistance increase rate
(%) volume increase rate
(%) Example 1 Pure Si 1A 0.3 2A 0.5 - - 72.6 49.5 45.1 Example 2 Pure Si 1A 0.3 2A 2 - - 74.8 47.7 42.4 Example 3 Pure Si 1A 0.3 2A 5 - - 84.9 40.3 37.9 Example 4 Pure Si 1A 0.3 2A 10 - - 86.4 38.5 35.6 Example 5 Pure Si 1A 10 2A 0.3 - - 76.1 45.8 40.1 Example 6 Pure Si 1A 0.3 2A 0.5 VC 2.5 68.3 62.3 55.6 Comparative Example 1 Pure Si - - - - - - 45.8 81.2 75.6 Comparative Example 2 Pure Si 1A 0.3 - - - - 53.4 69.1 64.8 Comparative Example 3 Pure Si - - 2A 0.5 - - 56.3 66.9 61.0 Comparative Example 4 Pure Si Z1 0.3 2A 0.5 - - 47.7 74.0 68.7 Comparative Example 5 Pure Si 1A 0.3 Z2 0.5 - - 42.6 83.6 78.2 Comparative Example 6-1 SiO+C 1A 0.3 2A 0.5 - - 60.2 64.3 58.3 Comparative Example 6-2 SiO+C 1A 0.3 - - - - 46.5 76.8 71.3 Comparative Example 6-3 SiO+C - - 2A 0.5 - - 49.1 72.1 66.3

Through the results in Table 4, it can be confirmed that when the first additive and the second additive of the present application are simultaneously included as electrolyte additives, it is effective in improving the performance after rapid charging of a lithium secondary battery using 100 wt% of Si as a negative electrode active material.

Specifically, the battery according to the present invention is used not only when neither the first additive nor the second additive is included (Comparative Example 1), but also when only the first additive or the second additive is used alone (Comparative Examples 2 and 3). ), it can be seen that the results are significantly improved in terms of capacity, resistance, and volume after rapid charging. In addition, the compound of Chemical Formula Z1 used in Comparative Example 4 had a minimal effect on improving fast charging performance compared to the first additive of the present invention, and the compound of Chemical Formula Z2 used in Comparative Example 5 actually worsened fast charging performance. You can check that. Additionally, in Comparative Example 6-1, which used a mixture of SiO and graphite instead of Si as the negative electrode active material, it can be seen that the capacity retention rate after rapid charging was low and the resistance increase rate and volume increase rate were high compared to Example 1.

Meanwhile, among Examples 1 to 6, it can be seen that the performance after rapid charging is the most excellent in Examples 3 and 4, where the weight ratio (W2/W1) of the second additive to the first additive is 15 or more.

Claims (13)

A non-aqueous electrolyte solution containing a lithium salt, an organic solvent, a first additive represented by the following Chemical Formula 1, and a second additive represented by the following Chemical Formula 2;
A positive electrode containing a positive electrode active material;
A negative electrode containing a negative electrode active material made of silicon; and
A lithium secondary battery comprising a separator interposed between the positive electrode and the negative electrode:
[Formula 1]

In Formula 1,
A is a heterocyclic group having 3 to 5 carbon atoms or a heteroaryl group having 3 to 5 carbon atoms,
R1 is an alkylene group having 1 to 3 carbon atoms,
[Formula 2]

In Formula 2,
R2 is an alkyl group having 1 to 10 carbon atoms substituted with one or more fluorines.
In claim 1,
A lithium secondary battery in Formula 1, wherein A is a nitrogen-containing heteroaryl group having 3 to 5 carbon atoms.
In claim 1,
R2 in Formula 2 is -(CR ₂ ) _n CF ₃ ,
R is hydrogen or fluorine,
A lithium secondary battery, where n is an integer from 0 to 9.
In claim 1,
The content of the first additive is 0.05% by weight to 10% by weight based on the total weight of the non-aqueous electrolyte solution.
In claim 1,
The content of the second additive is 0.1% by weight to 15% by weight based on the total weight of the non-aqueous electrolyte solution.
In claim 1,
A lithium secondary battery wherein the weight ratio of the second additive to the first additive is 1.5 or more.
In claim 1,
A lithium secondary battery, wherein the weight ratio of the second additive to the first additive is 6 or more.
In claim 1,
The non-aqueous electrolyte solution further includes at least one third additive selected from the group consisting of vinylene carbonate, 1,3-propane sultone, 1,3-propene sultone, and lithium difluorophosphate.
In claim 1,
A lithium secondary battery, wherein the organic solvent includes a mixture of a fluorinated cyclic carbonate-based solvent and a linear carbonate-based solvent.
In claim 9,
A lithium secondary battery, wherein the linear carbonate-based solvent includes diethyl carbonate, ethylmethyl carbonate, or a mixture thereof.
In claim 1,
A lithium secondary battery wherein the concentration of the lithium salt in the mixed solution of the lithium salt and the organic solvent is 1.5M or more.
In claim 1,
A lithium secondary battery, wherein the positive electrode active material includes a lithium composite transition metal oxide represented by the following Chemical Formula 3:
[Formula 3]
Li _1+x (Ni _a Co _b Mn _c M _d )O ₂
In Formula 3 above,
M is W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B and Mo. It is one or more selected from the group consisting of
1+x, a, b, c and d are the atomic fractions of each independent element,
-0.2≤x≤0.2, 0.60≤a<1, 0<b≤0.30, 0<c≤0.30, 0≤d≤0.10, a+b+c+d=1.
In claim 1,
The positive electrode active material is a lithium secondary battery comprising a lithium composite transition metal oxide having a molar ratio of nickel in the transition metal of 70 mol% or more.